Publication History: This article was written especially for "Crain's Petrophysical Handbook" by E. R. Crain, P.Eng in 202. This webpage version is the copyrighted intellectual property of the author.


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HYDROGEN BASICS
Hydrogen is the smallest and lightest element. At standard conditions hydrogen is a diatomic gas (H2). It is colorless, odourless, tasteless, non-toxic, and highly combustible, creating water (H2O) when burned. Hydrogen can be separated from water by electrolysis and from methane by pyrolysis or steam reforming. There is one known example of naturally occurring hydrogen in a reservoir setting, but dozens of hydrogen seeps are known around the World.

Most of the hydrogen on Earth exists in water and organic compounds. Known occurrences of natural hydrogen are rare, partly because we haven’t looked very hard due to preconceived opinions that are probably wrong.

Major uses of hydrogen are upgrading bitumen and heavy oil, and removal of sulphur from liquid petroleum. The use of hydrogen for lighter than air transportation was abandoned in 1937 after the dirigible Hindenburg caught fire. There are 1000s of other commercial uses in food preparation, plastics, and petrochemicals.

Hydrogen may be the wave of the future for powering land transportation and industry in the “Hydrogen Economy” – think 2050 or beyond. There are many unresolved technical and practical issues. The virtue of such a fuel is that the exhaust is water (and maybe some NOx) instead of CO2, which contributes to climate change. The exhaust water would have to be captured on the vehicle since that huge amount of water would have its own local climatic effects and would make roads totally useless at temperatures below freezing. Foreseeable but ignored consequences abound.

Petrophysics, with other geosciences, can play a role in finding and evaluating new naturally occurring hydrogen resources. Current production is by reforming of methane, electrolysis of water, or pyrolysis of methane. Petrophysics will play a major role in locating these raw materials if the hydrogen economy actually takes off.
 


The Colours of Hydrogen: green if produced from 100% renewables; black, brown, or grey if coal or methane is used; blue if CCS is added, gold or white if source is naturally occurring. (Image from World Economic Forum, from 2022 talk by Emanuele Taibi)


The Green Hydrogen Transition (Image courtesy International Renewable Energy Agency)

To produce enough Green Hydrogen to displace fossil fuels, we need to increase renewable electrical energy output by a factor of 1000, probably much more. And drill and complete unknown thousands of deep water wells, plus build a desalinization plant for each electrolysis plant. Why? Most of the fresh water needed for electrolysis is already allocated to human and agricultural use.

It might be better to electrify transport and use heat pumps for HVAC, and avoid the H2 middleman. This leaves about 40% of current carbon emissions to be fixed – the carbon-heavy industrial heartland to decarbonize with Green Hydrogen. As hydrogen technology improves, the timing might just work out for all those 2050 targets that governments have made.

HYDROGEN PRODUCTION
There are over 200 chemical reactions that can produce hydrogen, some dating back 150 years or so. None could be considered “Green”. About 48% of commercial bulk hydrogen is produced by the Steam Reforming Method (SRM), using natural gas as a feedstock, with CO2 release to the atmosphere, or with carbon capture and storage (CCS) to mitigate greenhouse gas (GHG) emissions.

Another large source is as a byproduct of the manufacture of ammonia, methanol, and other industrial chemicals. A tiny fraction is from electrolysis of water or pyrolysis of methane.

The 2015 discovery of naturally occurring hydrogen in Mali has broadened the search for clean green sources.

HYDROGEN PRODUCTION FROM METHANE USING STEAM REFORMING
The most common is reacting water, in the form of super-heated steam (700 – 1100 C), with methane to form carbon monoxide,, which in turn causes the removal of hydrogen from the methane. The water vapor is then reacted with the carbon monoxide to oxidize it to carbon dioxide, turning the water into hydrogen. The process is called Steam Reforming, also known as the Bosch process. The chemistry is:
1: CH4 + H2O → CO + 3 H2
2: CO + H2O → CO2 + H2

This reaction is favoured at low pressures but is usually conducted at high pressures (2.0 MPa). This is because high pressure H2 is the most marketable product, and pressure swing adsorption (PSA) purification systems work better at higher pressures. The product mixture is known as "synthesis gas" because it is often used directly for the production of methanol and related compounds.

HYDROGEN PRODUCTION FROM ELECTROLYSIS OF WATER
When a direct current is run through water, oxygen forms at the anode (+) while hydrogen forms at the cathode(-). Typically the cathode is made from platinum or another inert metal. While this a proven technology, it supplies only 5% of World demand for hydrogen.

The method presumes that an adequate supply of unallocated fresh water, (or desalinated sea water or medium, depth oilfield brine) and a source of unallocated electricity can be found. In many areas, fresh water is already in short supply and additional draws on surface or near surface water may be impossible. Deeper sources may also be restricted. See “Analyzing Water Wells” to learn how to locate potential underground sources of water.

The chemistry electrolysis is pretty simple:
3: 2 H2O + electricity → 2 H2 + O2 + heat

Theoretical efficiency (electricity used vs. energetic value of hydrogen produced) is between 88 – 94% with no impurities in the water, much less if desalinization is needed. Energy cost of co compression, storage, and transportation to market are also not included3.

HYDROGEN PRODUCTION FROM METHANE PYROLYSIS
Natural gas (methane) pyrolysis is a one-step process that produces no greenhouse gases. Developing volume production using this method is the key to enabling faster carbon reduction by using hydrogen in industrial processes, fuel cell electric heavy truck transportation, and in gas turbine electric power generation.

Pyrolysis is achieved by having methane (CH4) bubbled up through a molten metal catalyst containing dissolved nickel at 1,070 C. This causes the methane to break down into hydrogen gas and solid carbon, with no other byproducts (except those from maintaining the reactor at the high temperature required).

The chemistry is deceptively simple, but implementation is tricky.
4: CH4 + heat + catalyst → C + 2 H2

The industrial-quality solid carbon may be sold as manufacturing feedstock or permanently landfilled, it is not released into the atmosphere and there is no ground water pollution in the landfill.

Methane pyrolysis is in development and considered suitable for commercial bulk hydrogen production, assuming low cost methane is available as both feedstock and heat source. Further research continues in several laboratories and at least one pilot project.

NATIVE HYDROGEN FROM RESERVOIR ROCKS
Conventional wisdom says that hydrogen gas does not occur naturally in convenient reservoirs like oil and natural gas, because the small molecules could escape too easily. This is not the case, as a hydrogen reservoir is being exploited in the region of Bourakebougou in Mali, producing electricity for the surrounding villages.

Discovered in 2015 while drilling for water, natural hydrogen blew out with the artesian water. Analysis of the well Bougou-1 found the gas had a concentration of 98% pure hydrogen, with traces of methane, nitrogen, and helium. This is the purest naturally occurring hydrogen ever discovered.

Further exploratory wells were drilled and analyzed, including two 2500 meter fully cored stratigraphic holes, resulting in a second natural hydrogen gas field.

The hydrogen is trapped in 5 reservoir layers, each sealed by a lava flow. The hydrogen molecule is so small, it is possible that only unfractured igneous or evaporite minerals can form the impermeable seal needed for hydrogen.

This is where petrophysics cones to the rescue. Take a peak under the rug and see what might be waiting below all those salts, anhydrites, and volcanics you drilled through over the last 70 years. No, it won’t be that easy as you probably need a deep-seated source and a migration path – well logs can help there too.

It’s time for a paradigm shift for hydrogen!

Some scientists believe gas generation will continue for thousands of years, sustainably decarbonising the local community (who did not have much of a carbon footprint to begin with. This is highly speculative as it may have taken millions of years for the gas to migrate and accumulate from deep source rocks to these reservoirs. There are at least 7 possible mechanisms for the generation of hydrogen discussed in the reference paper.



Stratigraphic sequence of Mali natural hydrogen discovery



Cross-section of Mali natural hydrogen discovery
 

Reference:
“On generating a geological model for hydrogen gas in the southern Taoudeni Megabasin, Bourakebougou area, Mali” ACS Letters, 2016
Denis Briere and Tomas Jerzykiewicz, Chapman Consulting, Calgary AB Canada
https://doi.org/10.1190/ice2016-6312821.1

NATIVE HYDROGEN FROM SERPENTINIZATION REACTIONS
The hydrogen in the above example may have come from a newly discovered iron-rich source at a moderate depth, or from a much deeper and hotter source caused by serpentinization.

Serpentinization is a form of low temperature metamorphism driven largely by hydration and oxidation of olivine and pyroxene, creating serpentine minerals brucite, and magnetite. Under the unusual chemical conditions accompanying serpentinization, water is the oxidizing agent, and is itself reduced to hydrogen. This leads to further reactions that produce rare iron group native element minerals, such as awaruite and native iron, methane, and other hydrocarbon compounds, and hydrogen sulphide.
During serpentinization, large amounts of water are absorbed into the rock, increasing the volume, reducing the density and destroying the original structure. The density changes from 3.3 to 2.5 gm/cc with a concurrent volume increase on the order of 30 – 40%. The reaction is highly exothermic and rock temperatures can be raised by about 260 °C, providing an energy source for formation of non-volcanic hydrothermal vents.

Hydrogen is produced during the process of serpentinization. In this process, water protons (H+) are reduced by ferrous (Fe2+) ions provided by fayalite (Fe2SiO4). The reaction forms magnetite (Fe3O4), quartz (SiO2), and hydrogen (H2).
5: 3 Fe2SiO4 + 2 H2O → 2 Fe3O4 + 3 SiO2 + 3 H2 + heat
fayalite + water → magnetite + quartz + hydrogen

Laboratory studies of serpentinization at high temperature and pressure show how methane could be produced, lending some credence to deep-seated gas and oil generation and migration.
6: 18 Mg2SiO4 + 6 Fe2SiO4 + 26 H2O + CO2 → 12 Mg3Si2O5(OH)4 +4 Fe3O4 + CH4
forsterite + fayalite + water + carbon dioxide → serpentine + magnetite + methane

My 1954 grade 9 chemistry class didn’t get much past 2H2 + O2 → 2 H2O, but equation 6 looks OK to me.

Ocean seeps show both hydrogen and methane emissions. We just have to find them onshore, complete with reservoir and seal, as in the Mali example. There are more than 100 published reports of natural hydrogen seeps on land in a dozen countries, treated as curiosities across many years. Maybe they will lead to a new industry, just as the oil seeps of antiquity did.
Reference: Wikipedia

 

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